There is a great need for compositions which can be used as adhesive bases for untreated fabrics and reinforcing materials. Untreated fabrics and reinforcing materials are understood in this context as being fabrics and reinforcing materials that have not undergone special surface treatment for adhesion purposes, e.g. by means of coating processes from solution (impregnation processes) or using latex dips. The bond between the surface of the carrier material and the rubber must be sufficiently strong that it does not constitute the weak point in the composite system.
The direct reaction of the rubber with unpretreated carrier material and subsequent peroxide crosslinking is not known in the prior art. Analogous direct adhesion processes are only systems vulcanizable with sulfur, such as polychloroprene and nitrile rubber, described in Handbuch für die Gummiindustrie, 2nd Edition, 1991, p. 500, published by Bayer AG. The use of this process in peroxide vulcanized systems based on HNBR is not disclosed in the prior art.
In order to ensure good bonding of the actual rubber that is to be peroxide crosslinked to the carrier material, the latter must be pretreated. For the pretreatment, the carrier materials are treated, for example, with a latex or a solution, for the application of a so-called finishing layer. Such finishing layers contain several chemically different constituents. These generally consist of a rubber selected from the group consisting of polychloroprene, polyvinylpyridine, polybutadiene or polybutadiene copolymers, the copolymers being selected from the group consisting of acrylonitrile, styrene, or mixtures of those polymers. Furthermore, it is often appropriate to mix with the latex additional resins, such as resorcinol resins with hardeners such as formaldehyde (or formaldehyde donors) and optionally silane compounds. Such latices are referred to as RFL latex (resorcinol-formaldehyde latex).
The carrier material is immersed in the latex, dried and reacted fully, and then the actual rubber is vulcanized onto the carrier material so pretreated. Vulcanization can be carried out both with sulfur or sulfur systems and peroxide.
The fabrics impregnated with conventional latices based on polybutadiene or polybutadiene copolymers, polychloroprene or polyvinylpyridine exhibit distinct weaknesses, particularly after ageing, when peroxide crosslinked rubbers are used, which are employed in the next step of manufacture.
In order to improve the ageing properties, EP-B1 0 252 264 and U.S. Pat. No. 5,176,781 therefore disclose the use of latices based on partially hydrogenated HNBR and/or in combination with conventional latices with RFL systems.
For the production of the carrier materials so obtained and activated for adhesion to peroxide vulcanizable rubber mixtures, several successive dip cycles or immersion cycles are often necessary.
Accordingly, the present invention provides a composition which enables a HNBR rubber to be vulcanized directly onto the carrier material in question without having to pretreat the reinforcing material.